1. Field of the Invention
The present invention relates to an angular position sensor and more particularly to a linear non-contact angular position sensor for sensing the angular position of a pivotally mounted device, such as a throttle valve, which includes a magnetic sensing element, such as a Hall effect integrated circuit (IC) and a mechanical adjustment mechanism which includes integral temperature compensation that allows the sensitivity of the sensor to be adjusted without the need for potentiometers and the like to provide a generally linear output signal as a function of the angular position of the sensor over a relatively wide temperature range.
2. Description of the Prior Art
Angular position sensors are known to be used for various purposes including throttle position sensors for determining the angular position of a butterfly valve in a throttle body. An example of such a sensor is disclosed in U.S. Pat. No. 4,893,502. Such sensors are generally used to sense the angular position of the butterfly valve in the throttle body in order to control the amount of fuel applied to the combustion chamber of an internal combustion engine.
Various sensors for monitoring the angular position of a pivotally mounted device, such as a butterfly valve, are known. For example, various contact type sensors, such as electromechanical potentiometers are known. Such electromechanical potentiometers include an arcuately-shaped thick film resistive ink resistor and a movably mounted precious metal electrical wiper that is adapted to be mechanically coupled to a butterfly valve such that the relative position of the wiper relative to the resistor varies in accordance with the angular position of the butterfly valve. Such sensors are used to provide an electrical signal which varies as a function of the angular position of the butterfly valve.
There are various known problems with such sensors. For example, such sensors cannot be hermetically sealed due to the dynamic seal required between the butterfly valve shaft and the wiper inside the sensor housing. As is known in the art such dynamic seals are subject to wear over time and thus, can result in degraded sensor performance in time. As such, when such sensors are used in a relatively hostile environment, such as an under-hood environment, dirt, moisture and chemical fumes are known to ingress into the sensor housing and cause degradation and erratic operation of the sensor.
Some known sensors, such as the sensor disclosed in U.S. Pat. No. 4,893,502, avoid the problem of dynamic seals. More particularly, the '502 patent discloses a modified throttle body which incorporates the sensor therewithin. In order to provide access to the sensor, the throttle body is open on one end. The opening is closed by a cover that is secured to the throttle body by way of a plurality of fasteners forming a static seal. However, there are known problems with such static seals. For example, due to the vibration of an internal combustion engine, the fasteners may loosen over time, thus degrading the static seal and, in turn, the sensor.
Another problem with contact type sensors is that they are subject to wear. In particular, the wipers are known to move back and forth in contact across the thick film resistor a relatively large number of times over the expected lifetime of the sensor; perhaps millions of time. Such moving contact causes localized reductions of the thickness of the thick film resistor. Since resistance is a function of cross-sectional area, the reduction of the resistor thickness will change the local resistance value in the portion of the resistor which experiences the greatest amount of wear. As such, this causes drift of the output over time which affects the calibration and linearity of the sensor.
There are other problems with such contact sensors. For example, in some situations, for instance when the engine is run at a nearly constant speed, engine induced vibration can cause additional localized resistor wear, which, as discussed above, can affect the calibration and linear output of the sensor.
In an attempt to overcome the problems associated with such contact type angular position sensors, noncontact sensors have been developed. Moreover, due to the relatively hostile environment of an internal combustion engine, various magnetic sensors have been developed. For example, U.S. Pat. Nos. 3,118,108; 4,392,375 and 4,570,118 disclose magnetic angular position sensors which include two magnets and a magnetically sensitive device, such as a Hall effect device or a magneto-resistor.
However, there are various known problems with such sensors which utilize two magnets. For example, such sensors are relatively more expensive than sensors which utilize a single magnet. Also, calibration of such sensors is relatively difficult. In particular, conventionally available magnets are generally provided in quantity with tolerance ranges of about ten percent. A second magnet doubles the range of potential variability and thus makes calibration relatively more difficult.
Other known angular position sensors avoid the problems of two magnet sensors and utilize a single magnet and a magnetically sensitive device, such as a Hall effect device, for example, as disclosed in U.S. Pat. Nos. 3,818,292; 3,112,464; 4,89,502 and 4,570,118. Such single magnet angular position sensors rely on a varying air gap to vary the magnetic flux density applied to the Hall effect device in response to angular motion. However, the varying air gap of such sensors causes the output signal of the sensor to be exponential and thus relatively non-linear. In order to linearize the response, the magnets utilized with such sensors have been known to be formed from irregular shapes by various known foundry casting methods. However, such cast magnets are known to be rough having imperfections in their surfaces which contribute to part-to-part variation. The process for removing such imperfections is relatively time-consuming and thus adds significantly to the overall cost of the sensor.
Other known single magnet angular position sensors with a varying air gap utilize irregular-shaped magnet holders for skewing the position of the magnet relative to the rotational axis and the Hall effect element. Such irregular-shaped magnet holders add to the overall cost of the sensor and also make the sensor relatively difficult to calibrate.
Angular position sensors which utilize a single magnet and a non-varying air gap are also known, for example, as disclosed in U.S. Pat. No. 4,893,502. The angular position sensor disclosed therein includes a single magnet and a magnetic resistance element (MRE). In this embodiment, a circular magnet is rigidly secured directly to the butterfly valve shaft. The MRE is disposed within a modified throttle body at a fixed air gap relative to the circular magnet. An amplifying circuit with variable gain is used to calibrate the sensors by way of potentiometers or variable resistors. As is known in the art, the output of such potentiometers may vary with temperature or time. Due to the relatively wide operating temperature range of such a sensor in an internal combustion environment, for example, such potentiometers will drift and affect the overall calibration of the device. Another problem with such an arrangement is that the electrical connection between such a potentiometer and the amplifier circuit is known to be made by relatively large macro-scale electrical tracings on a printed circuit board which would be physically large enough to act as an antenna, thus making the circuit relatively susceptible to electromagnetic interference (EMI) and especially radio frequency interference (RFI). As such, the amplifying circuitry would have to be shielded which adds to the cost of the sensor.